Spatial Variation of Surface O3 Responses to Drought Over the Contiguous United...

Li, W., Y. Wang, J. Flynn, R. Griffin, F. Guo, and J. L. Schnell (2022), Spatial Variation of Surface O3 Responses to Drought Over the Contiguous United States During Summertime: Role of Precursor Emissions and Ozone Chemistry, J. Geophys. Res..

Drought is an extreme weather and climate event that has been shown to cause the worsening of ozone (O3) air pollution. Using 15-year (2005–2019) surface O3 observations and weekly US Drought Monitor (USDM) indices, this study estimated that summertime US-mean surface O3 increased by 1.47 ppb per USDM level. It is revealed that O3 responses to drought display a spatial east-west variation: higher O3 enhancement in the Southeast (2.24 ppb/USDM), and no significant change or even a decrease in the west (e.g., −0.06 ppb/ USDM in California). The diurnal changes of O3 with drought also show an opposite pattern between the Southeast and California. Formaldehyde (HCHO) and nitrogen dioxide (NO2) column, two satellite-based O3 precursors proxies, show an increasing rate of 0.41 × 1015 molec/cm2/USDM and 0.03 × 1015 molec/ cm2/USDM in the Southeast, respectively, while these rates are not statistically significant in California. We at the sites with long-term observations in California and Georgia. Isoprene concentrations decreased by ∼37% explained this spatial discrepancy from the perspective of O3 chemistry by applying a zero-dimensional model under exceptional drought in California causing a reduction of O3 production (PO3) by ∼23.7% during daytime. On the contrary, isoprene increased by ∼41% in Georgia inducing a consequent increase of PO3 by ∼33.4% which accounts for more than half of the O3 enhancement. This study reveals the key role of biogenic isoprene on ozone chemistry under drought conditions.

Research Program: 
Atmospheric Composition Modeling and Analysis Program (ACMAP)